As a technology for realizing a high speed data transmission in a mobile radio communication, a multiple input multiple output (MIMO) multiplexing system is proposed, for example. The MIMO is a technology for transmitting multiple signals by using a same frequency and time from multiple transmission antennas and receiving the signals by multiple reception antennas to be separated into individual signals.
As an example of a signal separation system appropriate to a reception apparatus configured to receive, on the basis of the MIMO, radio signals where an influence of a multipath interference is small such as an orthogonal frequency division multiplexing (OFDM), a maximum likelihood detection (MLD) processing is proposed. The MLD processing is a signal separation processing of generating replicas of all transmission antenna signals and selecting a most likely transmission antenna signal by using the generated replicas to remove an inter-antenna interference.
In contrast to this, in a reception apparatus configured to receive radio signals where the influence of the multipath interference is large such as a code division multiple access (CDMA), a large number of adjacent signals are taken into account. For this reason, a complexity of the MLD processing is increased in an exponential manner, and it is difficult to realize the configuration.
In view of the above, in the radio system where the influence of the multipath interference is large, a minimum mean square error (MMSE) processing is executed to remove the influence of the multipath interference before the execution of the MLD processing. The MMSE processing is a processing of suppressing an interference from the transmission antenna other than the focused transmission antenna by way of a linear filter. In order that the reception apparatus corresponds to both the radio system with the small influence of the multipath interference and the radio system with the large influence of the multipath interference, the reception apparatus may implement both the MMSE processing and the MLD processing in some cases. For example, Japanese Laid-open Patent Publication No. JP2006-339773 discloses a technique in which the MMSE processing is executed before the MLD processing.